"...it would be misleading to release a Biography on Hilary Tolkien without proper reference to his close relationship with his brother."

This suggests to me that the Tolkien Estate believed that there was too much planned emphasis on Hilary as J.R.R.Tolkien's brother -- whether in the writing, the title, or the proposed publicity campaign, is not clear.

Obviously, no one would write or read a full-length biography of Hilary Smith, humble farmer from the midlands. The only reason for the book is to take advantage of the market for books about Professor Tolkien, his works and his life. So inevitably the question becomes, when does this book become a trespass on the rights of the Tolkien Estate, which represents the interests of JRRT's descendants? The Estate obviously asked for changes that the author or publisher felt would damage the project fatally.